Cathode-ray tube



J. DE GIER CATHODE-RAY TUBE Nov. 4, 1952 Filed April 6,1951

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INVENTOR JOHANNES DE GIER BY %,M/%

AGENT Patented Nov. 4, 1952 CATHODE-RAY TUBE Johannes de Gier,-'Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application April 6, 1951, Serial No. 219,550 In the Netherlands May 2, 1950 6 claims. (01. 313-s2) 1- This invention relates to cathode ray tubes for television reception. 7 Such tubes often employ an ion trap to separate the negativev ions, which are emitted by the cathode together with the electrons or which are produced in the discharge space, from the electron beam, in order to avoid a so-called ion spot on the image screen. Such an iron trap employs means to deflect the electrons from their initial direction in which the ion beam maintains its initial direction, but alternatively the ions may be deflected in the same direction as the electrons, the separation of ions and electrons being effected by deflecting the electrons again into their initial direction. 1.

This particular construction avoids another disadvantage, which is generally inherent in cathode-ray tubes which are not provided with a deionisation device, but which is also found in tubes provided with an ion trap.

Direct light of the cathode visible on the screen of the cathode-ray tube has in the past been objectionable. In order to avoid the reflection of the light produced by the screen on the photoelectric cathode in image transformers, these two elements, instead of being arranged in parallel have been arranged at an angle in such manner that the light of the collecting screen no longer reaches the photo-electric cathode and such that the electrons are conveyed along curved paths from one element to the other. In order to avoid the ion spot, similar precautions have been taken with cathode ray tubes,'but in this case the tube was given a curved construction which was manufactured with difficulty, the arrangement of cylindrical coils, i. e. focussing coils, being difiicult.

It has been found that the type of screen bears to some extent upon the nature of the phenomenon. The disadvantage is more apparent in the case of thin collecting screens,which transmit a great quantity of light. not possible to employ certain types of screens,

Consequently, it is It is an object of the invention to eliminate cathode light in cathode-ray tubes for television reception.

According to the invention one or more transverse walls provided with an aperture are'arranged in the path transversed by the electrons from the cathode to the area where they leave the final anode in such manner that the part of the cathode which is intended to be heated to the temperature at which electron emission takes place is not visible from any point of the collecting screen.

Fig. 1 shows one form of light shield according to the invention;

Fig. 2 shows another embodiment of a light shield according to the invention;

Fig. 3 shows an electron beam focussing system in conjunction with a light shield;

Fig. 4 shows another electron beam focussing system with a light shield;

Fig. 5 shows a cathode-ray tube employing a light shield according to the invention.

Fig. 1 of the drawing shows one form of ion trap for separating ions from the electron beam in a cathode ray tube which comprises a cylindrical electrode l which embraces the electron beam emitted by a cathode 2.

This electrode, which is hereinafter referred 'to as an ion collector hasa transverse wall 3 (collecting plate). having an aperture 4 to allow the electrons to pass therethrough. The cylindrical part of the ion collector may be a metal body arranged in the tube, and need not necessarily have a circular section. Alternatively, it may be constituted by a conductive coating or a metal part of the tube wall.

The aperture 4 in the collecting plate 3 is usually circular and concentric with the axis of the ion collector, but neither of the aforementioned requirements for the aperture is absolutely necessary.

and, moreover due to the harmful phenomenon The end surface at the left-hand end of the cylinder 1 is at an angle to the axis 5 of the cylinder. At this end the electrode 6 is located, the end of which facing the cylinder is at a similar angle to the axis 5 so that a narrow gap is formed between these two parts in which a potential difference between the electrode 6 and the cylinder l produces an electric field, which has a constant component in the area covered by the beam at right angles to the axis 5, parallel to the plane of the drawing. The other end of electrode 6 is closed by a diaphragm I having a central aperture 8. The cathode 2 is surrounded by a Wehnelt cylinder 9, provided with a diaphragm 3 to, having a. central aperture ll. The beam 12 composed of electrons and negative ions is deflected in the direction of the arrow in the electric field between the electrode 6 and the cylinder I. The deflecting action of the electric field on the electron beam is neutralized by magnetic forces at right angles to the plane of the drawing. These forces do not change the direction of the ions, so that the ion beam ends at the inner wall'of the cylinder I.

Where the magnetic forces are strongest, the deflection of the electronlrieam from the axis 5 of the cylinder I is greatest. A transverse'pa'rtition I3 is arranged at this point in cylinder I which is provided with an eccentric aperture for the passage of the electron beam I4. By-choosing the point where the magnetic forces are acting it may be readily ensured that the eccentricity of this aperture is suflicient so that, viewed froidthe cathode, the "aperture in; the collecting platen 'is completely screened by-"the transverse l.', f'It is only necessary that the extension cf" the line connecting "the biottcim point 'of the aperture l-anathetop Point ofthe apertnre lcconstitute spasm boundaries of theapertures S and- 1 I inthe diaphragm l, and I'll. Consequently, the

1 am- ,cql' e i i l etfli d t e ib t j'part of the partition 13 may be ornittedifdesired. "Thelatter" may be constituted by astrip-of a a width equalto the diameter of the aperture irrthe collecting plate.

Referring to Fig. 2 the ion collector comprises "a bro'ken cylinder 115. having a circular sectional v field operates the ierem aretf the; cylinder, fthe-"lihes of' force of "which are at right angles it firlan ofi hei te r iT ea e m is deflectedby'this field-in the direction of the arrow through an'an'gle' such thatthe axis of the beam finally passes'throu'gh the-centercf the ""aperture 21 1in"i hej: 61 lecting plate 2 2f alld' is at jfl ght angles 'to"t'he-fp anef'of the collecting l late.

j Thejions being-"substantially i not influenced 1 by the magnetic field "continue ftravelling *in the airie directionfin the b en d or the cylin'derf'so thatthey striketlie wall oi'the cylinder.

, fascreenu rearranged in the bend'ofthe cylinder'which is"by-passed"by the electron beam and which intercepts the cathode light inthedirec- "ftiiin'bftheapertur inthe' contesting plate 22.

the semen arranged in"the"felectrically field-free space insidef'thecylinderfif'can' ex- "tend near to the path of the electrons, without acting upon the latter.

In t e e fbodiment shown inFigJSthebeam composedj of electrons and negative ions'passes gro n the cathode "through an immersion lens system, comprising controlelectrode 2 6 and accelerating azie' i e Between ey in'di-s' 21 and T523" an electric fieldiis produced; which concenimp ded focuses 'the electrons. The'cylinder through taste: the pathfoi the" electron beam between the :diaphragm "19ai'id the collecting "p1a'te3l. The electron'beamds thus deflected, the negative ions continue in. their initial path 32 located so far distant from the center of the electrode that it lies in the shadow of the diaphragm 29 outside the cone of cathode light cir- In the embodiment'of the electrode system shown in Fig. 4 the separation of negative ions from the electron beam occurs near cathode 33. Under the action of the combined influence of a magnetic lens fieldproduced by the coil 34 and ytheelectro-static field between control electrode 3% and'accelerating electrode 36 the electrons follow strongly converging paths. The negative ions aresubjected only to the action of the electro 'static 'fieldand thus the ion beam is made less convergent. The ion beam is indicated by a broken line whereas the path of the electrons is indicated by a full line. Collecting plate 31 is arranged at a predetermined distance 1 from the cathode and intercepts the ionb'ea'm. "I'lie point at'which the collecting plate 31 is located is chosen so that the sectionalareaof the ion beam is small relative to thesectiorial'aiea of the electronbeam, which is strongly spread inthis area.

'Thecollectirig 'p'late intercepts not'only the negativeions but'also part'of the electron beam, but

this partmay besmall with respect to the -total electron 'ciirrent. The electrons are concentrated in' a focus by 'a n electrostatic lens field between acceleratingelectrode36 and final anode 38. The final anode'aa isprovided with a circumscribihg diaphragm'39, havingan aperture 40. The area otthis diaphragm 'is"chosen'so that,viewed from the'cathoda the aperture!!! is completely screened-by thefcollecting plate3l.

The various electrode systems are adapted to be arranged in the straight'cylindrical' neck of a cathofi e-ray tube or the conventional construction. The systenrshown "in Fi'g.-"3-is arranged at an angle 'to the tube axis" 4 l as-shown in Fig; 5,

magnetic fields to deflect the beam in two directionsij at right j angles 'to' one another" in order-to 'scanthecollecting screen.

Whilefthe inv'entionhas"thus' b'een described in specific embodiments, "other modifications thereof win be readily" apparent to those skilled in the art without departing ird'mthe spiritand scope of the invention as defined "in the appended claims.

What I claim-"is: I H Y 1. Acathode- 'ray 'tfibefcr television reception anaemia gunimemdmg' a cathode for generating anel'ectron beam, in ion" trap in the path of the beam: and positioned to intercept ions in 'thefelectronbeam' by deflecting the electrons in a carted path, aftrafisverse wall 'p ovided'with anaprture 'tnerem'm the'path of (tlidelectron beam; and aftransverse wall element located between said cathode and s'aid aperture in said transversewall for interrupting the "path "of light' -ra ys radiated by said "cathode whe'reby said "l'ight' rays "are unable to pass through saidaperture.

2. A cathode-ray tube fortelevision reception comprising an electron gun'includinga cathode for generating an electron beam, an ion trap in the path of the beam and positioned to intercept ions in the electron beam by deflecting the electrons in a curved path, said ion trap comprising a hollow cylindrical electrode having a transverse wall element with an aperture therein for the passage of the electron beam, a transverse wall provided with an aperture therein in the path of the electron beam, and a transverse wall element located between said cathode and said aperture in said transverse wall for interrupting the path of light-rays radiated by said cathode whereby said light-rays are unable to pass through said aperture.

3. A cathode-ray tube for television reception comprising an electron gun including a cathode for generating an electron beam, an ion trap in the path of the beam and positioned to intercept ions in the electron beam by deflecting the electrons in a curved path, said ion trap comprising a hollow cylindrical electrode having a given axis, means to direct the electron beam into said cylindrical electrode at a given angle with said axis, a transverse wall element forming part of said cylindrical electrode and having an aperture for the passage of electrons in said beam, and a second transverse wall element forming part of said cylindrical electrode and provided with an aperture therein in the path of the electron beam, the aperture in said second wall element being located at a point at which the path of the electron beam is parallel to the said axis whereby the electron emissive portion of the cathode is not visible from the side of the second transverse wall portion remote from the gun.

4. A cathode-ray tube for television reception comprising an electron gun including a cathode for generating an electron beam, an ion trap in the path of the beam and positioned to intercept ions in the electron beam by deflecting the electrons in a curved path, said ion trap comprising a first hollow cylindrical electrode portion having a given axis and a second hollow cylindrical electrode portion having an axis, a first transverse wall element at the junction of said first and second electrode portions having an aperture therein for the passage of electrons in said beam, and a second transverse wall portion provided in the second cylindrical electrode portion and provided with an aperture therein in the path of the electron beam, the aperture of said second transverse wall portion being located at a point at which light-rays radiated by said cathode are unable to pass through said aperture.

5. A cathode-ray tube for television reception comprising an electron gun for generating an electron beam, an ion trap in the path of the beam and positioned to intercept ions in the electron beam by deflecting the electrons in a curved path, said ion trap comprising a hollow cylindrical electrode, a first transverse wall portion in the path of the beam and having an aperture for the passage of said beam, and a second transverse wall portion provided with an aperture therein in the path of the electron beam, the aperture in the second wall element being positioned to block visual alignment with the first wall element and the cathode whereby the electron gun emissive portion of the cathode is not visible from the side of the transverse wall remote from the gun.

6. A cathode-ray tube for television reception comprising an electron gun for generating an electron beam, an ion trap in the path of the beam and positioned to intercept ions in the electron beam by deflecting the electrons in a curved path, said ion trap comprising a hollow cylindrical electrode, a first transverse wall portion in the path of the beam and having an aperture therein eccentric to the axis of the electrode for the passage of the beam, and a second transverse wall portion spaced from the first wall element and provided with an aperture therein in the path of the electron beam, the aperture in the second wall element located on the axis of the electrode whereby the electron emissive portion of the cathode is non-visible from the side of the transverse wall remote from the gun.

JOI-IANNES DE GIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,099,749 Orth Nov. 23, 1937 2,099,846 Farnsworth Nov. 23, 1937 2,181,850 Nicoll Nov. 28, 1939 2,211,613 Bowie Aug. 13, 1940' 2,211,614 Bowie Aug. 13, 1940 2,341,764 De Gier Feb. 15, 1944 2,456,474 Wainwright Dec. 14, 1948 2,496,127 Kelar Jan. 31, 1950 2,555,850 Glyptis June 5, 1950 2,562,242 Pohle July 31, 1951 2,562,243 Pohle July 31, 1951 2,565,533 Szegho et a1 Aug. 28, 1951 2,580,355 Lempert Dec. 25, 1951 2,582,402 Szegho Jan. 15, 1952 

